Does the nucleosome associated DNA repeat length change during the in vitro differentiation of embryonal carcinoma (ec) cells to parietal endoderm? The DNA repeat length of ec cells and isolated primary parietal endoderm will be compared by limited micrococcal nuclease digestion of isolated nuclei and polyacrylamide gel electrophoresis. Do chromatin-associated nuclear proteins change when embryonal carcinoma cells differentiate to parietal endoderm? Total nuclear proteins, nuclear proteins released by limited digestion with pancreatic deoxyribonuclease I and micrococcal nuclease, and the HMG (high mobility group) and LMG (low mobility group) nuclear proteins will be compared in ec cells and parietal endodermal cells by SDS polyacrylamide gel electrophoresis. Antisera to endodermal specific nuclear proteins will be made and used to measure the appearance of the antigen during the in vitro differentiation of ec cells. Do parietal endodermal nuclei contain activities that will cause ec cells to differentiate to endoderm? Endodermal nuclear proteins will be introduced intra-cellularly into ec cells by cellular microinjection. The formation of parietal endodermal cells will be measured by the appearance of cells secreting plasminogen activator, synthesizing Reichart's membrane like material and having low alkaline phosphatase activity.